It is known that certain materials of unique utility and commercial value are in fact theoretically unstable under the normal conditions of their use; that is, they were formed in thermodynamic equilibrium under special conditions of temperature, pressure, magnetic field, etc., and then induced to remain in the same atomic or molecular configuration when the special conditions were removed. Such metastable, "frozen in" structures, thermodynamically out of equilibrium under normal conditions, are examplified by magnets, ordinary glasses, diamonds, cubic boron nitride, and many alloys. Recently it has been found that certain alloys can be temperature quenched extremely rapidly from the molten state to room temperature to produce metallic glasses--solids in which the normal crystalline structure has not had time to form. These materials often have unique and valuable properties. There is reason to believe that under certain conditions another field of new materials exists, comprising substances and/or compositions that can only be formed at high pressures, and having unique densities, internal structure, or other properties, and that may be obtained in a metastable state at ordinary conditions by a process that includes very rapid decompression--removal of the initial confining pressure at a rate so rapid that internal rearrangements of structure cannot be initiated.
Reference is made to an article entitled "Paramagnetic Properties In Pressure Quenched CdS," by R. M. MacCrone, et al., Solid State Coms., Vol. 35 pp. 615-618, Pergamon Press Ltd., 1980. In this article cadmium sulfide was compressed to a pressure above 40 kilobars and then decompressed with a rate "approaching 5.times.10.sup.6 bars per second," or in about 1/25 of a second. It appears that the resulting CdS was at least in part in a different physical form which is metastable and exhibits properties which differ from the normal physical and magnetic properties of cadmium sulfide at room temperatures. However, the relatively slow reduction in pressure of 1/25 second is such that most materials will revert to their normal low pressure state in the course of the reduction in pressure.
Accordingly, a principal object of the present invention is to produce metastable substances or compositions by a process which includes rapid decompression. A further object is to provide a suitable apparatus in which such a process can be safely and usefully carried out.